The present invention claims the priority of the German patent application 197 50 057.9-16 dated Dec. 11, 1997, the disclosure of which is also made expressly the subject matter of the present invention.
The invention relates to a mold-closing unit for an injection molding machine for processing plastic materials and other plasticisable masses such as e.g. ceramic masses, powdery masses and the like.
From Patent Abstract of Japan, vol. 14 no. 206 (M-0967) and the associated JP 02.045111A is known a device which can also be used, for example, for serial closing in connection with a mold closing unit. First, with a first device, a mobile mold carrier is transferred roughly until the closure of the mold with the stationary mold carrier, whilst the actual locking pressure is then applied by an additional device. As the first device, a shaft is provided which is mounted rotatable in relation to a supporting element. Via a second device, additional forces can be transmitted via the shaft. In order here to decouple as far as possible the force-transmitting threaded parts from the force flux, a switching chamber is disposed between supporting element and the force transmission element. If the switching chamber is placed under pressure, the rotation of the shaft is halted and the pressure transmitted via the shaft itself as the force transmission element. The switching chamber can admittedly be influenced as desired in order to obtain any freely switchable transition between the first and second devices before or after the mold halves come into contact with one another, such that the transition is no longer dependent on the position of the first device. Similarly, the spacing between the parts coming into contact with one another can be eliminated at any time independently of an additionally necessary deformation. What is ensured there, however, is merely that the shaft no longer rotates; the drive components are nevertheless subjected to all the forces.
From EP-A 674 985 is known a mold-closing unit in which serial closing is realized. In order to decouple the first device and more especially the spindle drive used there from the force flux occurring during the building up of the locking forces, according to FIG. 2 there, resilient restraining means in the form of springs are provided. When a pre-determined force is exceeded, the latter ensure that the spindle drive is secured against passive reverse rotation and the forces no longer burden the drive of the first device. The springs provided for this purpose have predetermined unalterable spring powers such that, once the springs have been fitted, the first device has to summon up the predetermined force independently of the injection part or of the other machine parameters. This force would only be alterable by exchanging the springs serving as decoupling means for softer or harder springs. Only when the force of the restraining means is overcome by the second device and thus a deformation necessary for this has occurred, do these restraining means have no more influence on the locking pressure, such that only from this point in time does the locking pressure become controllable and adjustable. Without a counter-force necessary for the deformation, decoupling of the first device and thus a transition to the second device cannot take place.
From U.S. Pat. No. 3,712,774 is known a hydraulic mold height adjusting device in which, behind a toggle lever mechanism, a bearing arrangement of the toggle lever mechanism is moveable hydraulically in the closing direction. The system can then be held tight in a once fixed position. Serial closing or influencing of the locking pressure does not result from this.
From U.S. Pat. No. 3,910,736 is known for a toggle lever a bearing arrangement of the force transmission elements, configured as bars, in hydraulic pads. The pressure in these hydraulic pads is adjustable and can, when exceeded, be relieved via a back-pressure valve. These pressure pads are intended to apply the locking force such that admittedly serial closing can take place if necessary but decoupling of the first device is not possible for the simple reason that the hydraulic pads are disposed on the side of the mold-closing unit opposite the toggle lever mechanism.
Proceeding from this prior art, the object underlying the present invention is to further develop a mold-closing unit of the type mentioned initially in such a way that optimal adaptation of the components to the respective requirements is rendered possible.
A mold-closing unit for an injection molding machine for processing plastic materials and other plasticisable masses is provided. The mold-closing unit includes: a stationary mold carrier; a mobile mold carrier; a mold tentering space formed between the mobile mold carrier and the stationary mold crier and adapted to receive parts of a mold; a first device for electromechanically moving the mobile mold carrier to and from the stationary mold carrier, with at least one rotatable element and a non-rotatable element co-operating therewith; a second device capable of being actuated after the first one, during the closure of the mold to build up the locking pressure; at least one supporting element to support at least the first device and connected to the stationary mold carrier by transmission elements, after actuation of the first device, the parts of the mold being at least almost in abutment as the mold is being closed, whilst the second device is provided mainly to build up the locking pressure on actuation; the rotatable element of the first device being mounted rotatable under the effect of a decoupling means and, as the locking pressure is built up by the second device the rotatable element abuts against one of the parts, comprising supporting element, non-rotatable elements of the first device or mobile mold carrier, wherein the rotatable element is decoupled from the force flux; a force transmission element to transmit the forces arising as the locking pressure is built up to the mobile mold carrier; a switching chamber, configured as the decoupling means and capable of being actuated by a hydraulic medium, being disposed between the force transmission element and either the supporting element or the mobile mold carrier, which switching chamber enables under pressure the rotation of the rotatable element, the pressure of the hydraulic medium in the switching chamber is freely actuatable, allowing a switchable transition between the first device and the second device; and a pressure pipe, configured as the force transmission element, lay overcoming a spacing, maintained by the switching chamber which is actuated by pressure, comes into contact with a spindle head of a shaft which is configured as the rotatable element of the first device.
In order to decouple the first device from the forces, which arise during the mold closure, an additional pressure pipe is now provided. If the spacing maintained by the switching chamber which is actuated by pressure is eliminated, not only is the shaft brought to a halt, simultaneously the pressure pipe is now used as an additional force transmission element. By this means, the pressure pipe can be dimensioned to the considerably higher forces which are necessary when the mold is closed, whilst the shaft can be dimensioned to the lower forces which occur as the mold is being closed and opened. The shaft is thus designed primarily to rotate as a positioning system which simultaneously contributes to reducing the masses to be moved in a rotatory manner. The force applied in the switching chamber positions the first device but can also equalize dynamic travel forces which occur during the movement of the mobile mold carrier.